FIG. 6 is a sectional view showing a conventional aluminum electrolytic capacitor as one example of a capacitor related to the present invention. FIG. 7 is a developed perspective view of a capacitor element constituting the aluminum electrolytic capacitor. In FIGS. 6 and 7, the reference numeral 10 indicates a capacitor element. This capacitor element 10 comprises an anode foil 12, a cathode foil 13, and a separator 14 interposed therebetween, which are wound together and formed as a roll-shaped structure. A pair of leader lines 15 are joined to the anode foil 12 and the cathode foil 13, respectively. Each of the leader lines 15 includes a copper-undercoated and tin-plated iron wire 15c extending outside from the capacitor element 10.
The reference numeral 16 indicates a cylindrical metal case made of aluminum. The metal case 16 has a closed bottom and an open top end. The capacitor element 10 is received in the metal case 16 together with a driving electrolyte (not shown). The reference numeral 17 indicates a sealing member for sealing the open top end of the metal case 16. The sealing member 17 is formed with a pair of through-holes allowing the corresponding iron wires 5c of the leader lines 15 to penetrate therethrough and extend outside from the capacitor element 10.
As best shown in FIG. 8, each of the leader lines 15 also includes an aluminum elongated round-bar-shaped portion 15a having one end formed with a recess (not shown). The iron wire 15c is inserted into the recess, and joined to the round-bar-shaped portion 15a with welding or the like. The other end of the round-bar-shaped portion 15a is flattened to provide a flat portion 15b. This flat portion 15b is joined to the anode foil 12 (or the cathode foil 13). The flat portion 15b of the leader line 15 is joined to the anode foil 12 in a plurality of joint sections 15d by means of ultrasonic welding, caulking or pressure welding.
In this connection, Japanese Patent Laid-Open Publication No. 2000-12386 can be referred to for reference as a published document related to this application.
As described above, in the conventional aluminum electrolytic capacitor, the joint between the anode and cathode foils 12, 13 and the corresponding leader lines 15 is achieved by means of ultrasonic welding, caulking or pressure welding. For example, a joint section formed by ultrasonic welding, or an ultrasonic-welded joint section, is intermetallically bonded together. Thus, the ultrasonic-welded joint section can advantageoulsy have a low resistance, and the resistance value can be reliably maintained without deterioration even under harsh conditions such as conditions of a reliabilit test. However, the ultrasonic-welded joint section involves problems of difficulty in obtaining a sufficient joint strength due to adverse affects from a dielectric oxide layer (not shown) formed on the surface of the anode foil 12, and attachment of foreign matters due to sparks generated during welding.
While a joint section formed by caulking, or a caulked joint section, can advantageously provide a sufficient joint strength, the caulked joint section has a relatively high resistance, and the strength of the anode and cathode foils 12, 13 is inevitably reduced due to the need for subjecting them to perforating. Thus, the caulked joint cannot be applied to small-size capacitors.
As with the ultrasonic-welded joint section, a joint section formed by pressure welding, or a pressure-welded joint section, can be intermetallically bonded to advantageously allow the joint section to have a low resistance which is reliably maintained without deterioration even under harsh conditions. However, the pressure-welded joint section has a joint strength inferior to that of the ultrasonic-welded joint section or caulked-joint section.
Each of the above joining means has both advantages and disadvantages, and it is difficult to meet all requirements. Thus, practically, there has been no choice but to select a suitable one of the joining means with respect to each type of capacitor.
Further, in the conventional aluminum electrolytic capacitor, the sealing member 17 is formed with the pair of through-holes for allowing the corresponding anode and cathode leader lines 15 to penetrate through and extend outside. Thus, when the aluminum electrolytic capacitor is used under high-temperature and high-humidity conditions, the pair of through-holes formed in the sealing member 17 is likely to cause deterioration in sealing against the driving electrolyte impregnated in the capacitor element 10.